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			<h1>Java 基础语法</h1>
<p>一个 Java 程序可以认为是一系列对象的集合，而这些对象通过调用彼此的方法来协同工作。下面简要介绍下类、对象、方法和实例变量的概念。</p>
<ul>
	<li>
		<strong>对象</strong>：对象是类的一个实例，有状态和行为。例如，一条狗是一个对象，它的状态有：颜色、名字、品种；行为有：摇尾巴、叫、吃等。</li>
	<li>
		<strong>类</strong>：类是一个模板，它描述一类对象的行为和状态。</li>
	<li>
		<strong>方法</strong>：方法就是行为，一个类可以有很多方法。逻辑运算、数据修改以及所有动作都是在方法中完成的。</li>
	<li>
		<strong>实例变量</strong>：每个对象都有独特的实例变量，对象的状态由这些实例变量的值决定。</li>
</ul><hr>
<h2>第一个Java程序</h2>
<p>下面看一个简单的 Java 程序，它将输出字符串 <em>Hello World</em></p>
<div class="example"> 
<h2 class="example">实例</h2> 
<div class="example_code">
<div class="hl-main"><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">HelloWorld</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
    </span><span class="hl-comment">/*</span><span class="hl-comment"> 第一个Java程序
     * 它将输出字符串 Hello World
     </span><span class="hl-comment">*/</span><span class="hl-code">
    </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">main</span><span class="hl-brackets">(</span><span class="hl-identifier">String</span><span class="hl-brackets">[</span><span class="hl-brackets">]</span><span class="hl-code"> </span><span class="hl-identifier">args</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
        </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">Hello World</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">; </span><span class="hl-comment">//</span><span class="hl-comment"> 输出 Hello World</span><span class="hl-comment"></span><span class="hl-code">
    </span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-brackets">}</span></div>
</div>
<br>
<a target="_blank" href="../try/runcode.php?filename=HelloWorld2&type=java" class="showbtn" rel="noopener noreferrer">运行实例 »</a>
</div><p><img decoding="async" src="https://www.runoob.com/wp-content/uploads/2013/12/662E827A-FA32-4464-B0BD-40087F429E98.jpg"></p>

<p>下面将逐步介绍如何保存、编译以及运行这个程序：</p>
<ul>
	<li>
		打开代码编辑器，把上面的代码添加进去；</li>
	<li>
		把文件名保存为：HelloWorld.java；</li>
	<li>
		打开 cmd 命令窗口，进入目标文件所在的位置，假设是 C:\</li>
	<li>
		在命令行窗口输入 <span class="marked">javac HelloWorld.java</span>  按下回车键编译代码。如果代码没有错误，cmd 命令提示符会进入下一行（假设环境变量都设置好了）。</li>
	<li>
		再键输入 <span class="marked">java HelloWorld</span> 按下回车键就可以运行程序了</li>
</ul>
<p>你将会在窗口看到 Hello World</p>
<pre>
$ javac HelloWorld.java
$ java HelloWorld 
Hello World
</pre>
<p>如果遇到编码问题，我们可以使用 <span class="marked">-encoding</span> 选项设置 <strong>utf-8</strong> 来编译：</p>
<pre>javac -encoding UTF-8 HelloWorld.java 
java HelloWorld </pre>
<p>Gif 图演示：</p>
<img decoding="async" src="//www.runoob.com/wp-content/uploads/2013/12/java-HelloWorld.gif">
<hr>
<h2>基本语法</h2>
<p>编写 Java 程序时，应注意以下几点：</p>
<ul>
	<li>
		<strong>大小写敏感</strong>：Java 是大小写敏感的，这就意味着标识符 Hello 与 hello 是不同的。</li>
	<li>
		<strong>类名</strong>：对于所有的类来说，类名的首字母应该大写。如果类名由若干单词组成，那么每个单词的首字母应该大写，例如 <strong>MyFirstJavaClass</strong> 。</li>
	<li>
		<strong>方法名</strong>：所有的方法名都应该以小写字母开头。如果方法名含有若干单词，则后面的每个单词首字母大写。</li>
	<li>
		<strong>源文件名</strong>：源文件名必须和类名相同。当保存文件的时候，你应该使用类名作为文件名保存（切记 Java 是大小写敏感的），文件名的后缀为 <strong>.java</strong>。（如果文件名和类名不相同则会导致编译错误）。</li>
	<li>
		<strong>主方法入口</strong>：所有的 Java 程序由 <strong>public static void main(String[] args)</strong> 方法开始执行。</li>
</ul>

<hr>
<h2>Java 标识符</h2>
<p>Java 所有的组成部分都需要名字。类名、变量名以及方法名都被称为标识符。</p>
<p>关于 Java 标识符，有以下几点需要注意：</p>
<ul>
	<li>
		所有的标识符都应该以字母（A-Z 或者 a-z）,美元符（$）、或者下划线（_）开始</li>
	<li>
		首字符之后可以是字母（A-Z 或者 a-z）,美元符（$）、下划线（_）或数字的任何字符组合</li>
	<li>
		关键字不能用作标识符</li>
	<li>
		标识符是大小写敏感的</li>
	<li>
		合法标识符举例：age、$salary、_value、__1_value</li>
	<li>
		非法标识符举例：123abc、-salary</li>
</ul><hr>
<h2>Java修饰符</h2>
<p>
	像其他语言一样，Java可以使用修饰符来修饰类中方法和属性。主要有两类修饰符：</p>
<ul>
	<li>访问控制修饰符 : default, public , protected, private</li>
	<li>非访问控制修饰符 : final, abstract, static, synchronized </li>
</ul>
<p>
	在后面的章节中我们会深入讨论 Java 修饰符。</p><hr>
	<h2>
	Java 变量</h2>
Java 中主要有如下几种类型的变量<br />
<ul>
	<li>局部变量</li>
	<li>类变量（静态变量）</li>
	<li>成员变量（非静态变量）</li>
</ul><hr>
<h2>Java 数组</h2>
<p>数组是储存在堆上的对象，可以保存多个同类型变量。在后面的章节中，我们将会学到如何声明、构造以及初始化一个数组。</p><hr>
<h2>Java 枚举</h2>
<p>Java 5.0引入了枚举，枚举限制变量只能是预先设定好的值。使用枚举可以减少代码中的 bug。</p>
<p>例如，我们为果汁店设计一个程序，它将限制果汁为小杯、中杯、大杯。这就意味着它不允许顾客点除了这三种尺寸外的果汁。</p>

<h3>实例</h3>
<div class="example">
<div class="example_code">
<div class="hl-main"><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">FreshJuice</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
   </span><span class="hl-identifier">enum</span><span class="hl-code"> </span><span class="hl-identifier">FreshJuiceSize</span><span class="hl-brackets">{</span><span class="hl-code"> </span><span class="hl-identifier">SMALL</span><span class="hl-code">, </span><span class="hl-identifier">MEDIUM</span><span class="hl-code"> , </span><span class="hl-identifier">LARGE</span><span class="hl-code"> </span><span class="hl-brackets">}</span><span class="hl-code">
   </span><span class="hl-identifier">FreshJuiceSize</span><span class="hl-code"> </span><span class="hl-identifier">size</span><span class="hl-code">;
</span><span class="hl-brackets">}</span><span class="hl-code">
 
</span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">FreshJuiceTest</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
   </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">main</span><span class="hl-brackets">(</span><span class="hl-identifier">String</span><span class="hl-brackets">[</span><span class="hl-brackets">]</span><span class="hl-code"> </span><span class="hl-identifier">args</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
      </span><span class="hl-identifier">FreshJuice</span><span class="hl-code"> </span><span class="hl-identifier">juice</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">FreshJuice</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-identifier">juice</span><span class="hl-code">.</span><span class="hl-identifier">size</span><span class="hl-code"> = </span><span class="hl-identifier">FreshJuice</span><span class="hl-code">.</span><span class="hl-identifier">FreshJuiceSize</span><span class="hl-code">.</span><span class="hl-identifier">MEDIUM</span><span class="hl-code">  ;
   </span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-brackets">}</span></div>
</div>
</div>
<p><strong>注意：</strong>枚举可以单独声明或者声明在类里面。方法、变量、构造函数也可以在枚举中定义。</p>
<hr>
<h2>
Java 关键字
</h2>
<p>
下面列出了 Java 关键字。这些保留字不能用于常量、变量、和任何标识符的名称。
</p>
<table class="reference">
<tbody><tr>
<th>类别</th>
<th>关键字</th>
<th>说明</th>
</tr>
<tr>
<td rowspan="4" align="center">访问控制</td>
<td>private</td>
<td>私有的</td>
</tr>
<tr>
<td>protected</td>
<td>受保护的</td>
</tr>
<tr>
<td>public</td>
<td>公共的</td>
</tr>
<tr>
<td>default </td>
<td>默认</td>
</tr>
<tr>
<td rowspan="13" align="center">类、方法和变量修饰符</td>
<td>abstract</td>
<td>声明抽象</td>
</tr>
<tr>
<td>class</td>
<td>类</td>
</tr>
<tr>
<td>extends</td>
<td>扩充,继承</td>
</tr>
<tr>
<td>final</td>
<td>最终值,不可改变的</td>
</tr>
<tr>
<td>implements</td>
<td>实现（接口）</td>
</tr>
<tr>
<td>interface</td>
<td>接口</td>
</tr>
<tr>
<td>native</td>
<td>本地，原生方法（非 Java 实现）</td>
</tr>
<tr>
<td>new</td>
<td>新,创建</td>
</tr>
<tr>
<td>static</td>
<td>静态</td>
</tr>
<tr>
<td>strictfp</td>
<td>严格,精准</td>
</tr>
<tr>
<td>synchronized</td>
<td>线程,同步</td>
</tr>
<tr>
<td>transient</td>
<td>短暂</td>
</tr>
<tr>
<td>volatile</td>
<td>易失</td>
</tr>
<tr>
<td rowspan="11" align="center">程序控制语句</td>
<td>break</td>
<td>跳出循环</td>
</tr>
<tr>
<td>case</td>
<td>定义一个值以供 switch 选择</td>
</tr>
<tr>
<td>continue</td>
<td>继续</td>
</tr>

<tr>
<td>do</td>
<td>运行</td>
</tr>
<tr>
<td>else</td>
<td>否则</td>
</tr>
<tr>
<td>for</td>
<td>循环</td>
</tr>
<tr>
<td>if</td>
<td>如果</td>
</tr>
<tr>
<td>instanceof</td>
<td>实例</td>
</tr>
<tr>
<td>return</td>
<td>返回</td>
</tr>
<tr>
<td>switch</td>
<td>根据值选择执行</td>
</tr>
<tr>
<td>while</td>
<td>循环</td>
</tr>
<tr>
<td rowspan="6" align="center">错误处理</td>
<td>assert</td>
<td>断言表达式是否为真</td>
</tr>
<tr>
<td>catch</td>
<td>捕捉异常</td>
</tr>
<tr>
<td>finally</td>
<td>有没有异常都执行</td>
</tr>
<tr>
<td>throw</td>
<td>抛出一个异常对象</td>
</tr>
<tr>
<td>throws</td>
<td>声明一个异常可能被抛出</td>
</tr>
<tr>
<td>try</td>
<td>捕获异常</td>
</tr>
<tr>
<td rowspan="2" align="center">包相关</td>
<td>import</td>
<td>引入</td>
</tr>
<tr>
<td>package</td>
<td>包</td>
</tr>
<tr>
<td rowspan="8" align="center">基本类型</td>
<td>boolean</td>
<td>布尔型</td>
</tr>
<tr>
<td>byte</td>
<td>字节型</td>
</tr>
<tr>
<td>char</td>
<td>字符型</td>
</tr>
<tr>
<td>double</td>
<td>双精度浮点</td>
</tr>
<tr>
<td>float</td>
<td>单精度浮点</td>
</tr>
<tr>
<td>int</td>
<td>整型</td>
</tr>
<tr>
<td>long</td>
<td>长整型</td>
</tr>
<tr>
<td>short</td>
<td>短整型</td>
</tr>

<tr>
<td rowspan="3" align="center">变量引用</td>
<td>super</td>
<td>父类,超类</td>
</tr>
<tr>
<td>this</td>
<td>本类</td>
</tr>
<tr>
<td>void</td>
<td>无返回值</td>
</tr>
<tr>
<td rowspan="3" align="center">保留关键字</td>
<td>goto</td>
<td>是关键字，但不能使用</td>
</tr>
<tr>
<td>const</td>
<td>是关键字，但不能使用</td>
</tr>

</tbody></table>
<p><strong>注意：</strong>Java 的 null 不是关键字，类似于 true 和 false，它是一个字面常量，不允许作为标识符使用。</p>
<hr>
<h2>
Java注释</h2>
<p>类似于 C/C++、Java 也支持单行以及多行注释。注释中的字符将被 Java 编译器忽略。</p>
<div class="example">
<div class="example_code">
<div class="hl-main"><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">HelloWorld</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
   </span><span class="hl-comment">/*</span><span class="hl-comment"> 这是第一个Java程序
    * 它将输出 Hello World
    * 这是一个多行注释的示例
    </span><span class="hl-comment">*/</span><span class="hl-code">
    </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">main</span><span class="hl-brackets">(</span><span class="hl-identifier">String</span><span class="hl-brackets">[</span><span class="hl-brackets">]</span><span class="hl-code"> </span><span class="hl-identifier">args</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
       </span><span class="hl-comment">//</span><span class="hl-comment"> 这是单行注释的示例</span><span class="hl-comment"></span><span class="hl-code">
       </span><span class="hl-comment">/*</span><span class="hl-comment"> 这个也是单行注释的示例 </span><span class="hl-comment">*/</span><span class="hl-code">
       </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">Hello World</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">; 
    </span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-brackets">}</span></div>
</div>
</div><hr>
<h2>Java 空行</h2>
<p>空白行或者有注释的行，Java 编译器都会忽略掉。</p><hr>

<h2>
	继承</h2>
<p>在 Java 中，一个类可以由其他类派生。如果你要创建一个类，而且已经存在一个类具有你所需要的属性或方法，那么你可以将新创建的类继承该类。</p>
<p>
利用继承的方法，可以重用已存在类的方法和属性，而不用重写这些代码。被继承的类称为超类（super class），派生类称为子类（sub class）。</p><hr>
<h2>接口</h2>
<p>在 Java 中，接口可理解为对象间相互通信的协议。接口在继承中扮演着很重要的角色。</p>
<p>
接口只定义派生要用到的方法，但是方法的具体实现完全取决于派生类。</p>

<hr>
<h2>Java 源程序与编译型运行区别</h2>
<p>如下图所示：</p>
<p><img decoding="async" src="//www.runoob.com/wp-content/uploads/2013/12/ZSSDMld.png"></p>
<p>
下一节介绍 Java 编程中的类和对象。之后你将会对 Java 中的类和对象有更清楚的认识。</p>			<!-- 其他扩展 -->
						
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<div id="postcomments"  style="display:none;" >
	<ol class="commentlist">
		<li class="comment byuser comment-author-tianqixin bypostauthor even thread-even depth-1" id="comment-16092"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Android</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;297***4077@qq.com</p></div><div id="runoobvote-id-16092" data-commid = "16092" class="upvotejs"><a class="upvote"></a> <span class="count">745</span></div></div><div class="comt-main" id="div-comment-16092"><p>标识符可以用来标识变量名、类名、类中的方法名和文件名等。
</p>
<p><strong>命名规则：</strong></p>
<ul><li>
(1) 由字母、数字、下划线、$组成，不能以数字开头。
</li><li>
(2) 大小写敏感。
</li><li>
(3) 不得使用java中的关键字和保留字。
</li></ul>
<p>关键字：都是小写的，jdk1.2多了strictfp(经准浮点型)，关键字 jdk1.4多了assert(断言)关键字，jdk1.5多了enum(枚举) 关键字。</p>

<p>true、false、null 严格说不应该算关键字，应称其为保留字更合适。
</p>
<p><strong>习惯：</strong></p>
<ul><li>
(1) 标识符要符合语义信息。
</li><li>
(2) 包名所有字母小写。
</li><li>
(3) 类名每个单词首字母大写，其它小写，如：TarenaStudent。
</li><li>
(4) 变量和方法：第一个单词小写，从第二个单词开始首字母大写，如：tarenaStudent。
</li><li>
(5) 常量：所有字母大写，每个单词之间用 <span class="marked">_</span> 连接。
</li></ul>


<p><strong>常用的转义字符：</strong></p>
<pre>
"\b" (退格)
"\f" (换页)
"\n" (换行)
"\r" (回车)
"\t" (水平制表符(到下一个tab位置))
"\' " (单引号)
"\" " (双引号) 
"\\" (反斜杠)
</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Android</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Android</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;297***4077@qq.com</p></div></span>6年前 (2017-08-10)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-18227"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;amy</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;143***9399@qq.com</p></div><div id="runoobvote-id-18227" data-commid = "18227" class="upvotejs"><a class="upvote"></a> <span class="count">392</span></div></div><div class="comt-main" id="div-comment-18227"><p>Java的八种基本类型：（按字节来分）</p><p>boolean&nbsp; &nbsp;布尔型&nbsp; &nbsp;1个字节 8bit（8位）</p><p>byte&nbsp; &nbsp; &nbsp;字节类型&nbsp; &nbsp;1个字节</p><p>char&nbsp; &nbsp; &nbsp;字符类型&nbsp; &nbsp;2个字节</p><p>short&nbsp; &nbsp; &nbsp;短整型&nbsp; &nbsp; &nbsp;2个字节</p><p>int&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 整型&nbsp; &nbsp; &nbsp; &nbsp; 4个字节</p><p>float&nbsp; &nbsp; &nbsp; 浮点型（单精度）4个字节</p><p>long&nbsp; &nbsp; &nbsp; 长整型&nbsp; &nbsp; &nbsp; 8个字节</p><p>double&nbsp; &nbsp;双精度类型&nbsp; 8个字节</p><p>Java中默认的整数类型是int，如果要定义为long ，则要在数值后加上L或者l</p><p>默认的浮点型是双精度浮点，如果要定义float，则要在数值后面加上f或者F</p><p>一个字节等于8位，1个字节等于256个数。2^8</p><p>一个英文字母或者阿拉伯数字占一个字节</p><p>一个汉字占2个字节</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">amy</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;amy</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;143***9399@qq.com</p></div></span>6年前 (2017-09-28)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-22721"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;jinling</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;103***5512@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://www.cnblogs.com/maowang1991/archive/2013/06/29/3162366.html">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-22721" data-commid = "22721" class="upvotejs"><a class="upvote"></a> <span class="count">373</span></div></div><div class="comt-main" id="div-comment-22721"><p><strong>一、命名规范</strong></p>

<p>1、 项目名全部小写</p>

<p>2、 包名全部小写</p>

<p>3、 类名首字母大写，如果类名由多个单词组成，每个单词的首字母都要大写。如：<span class="marked">public class MyFirstClass{}</span></p>



<p>4、 变量名、方法名首字母小写，如果名称由多个单词组成，每个单词的首字母都要大写。如：</p>

<pre>int index=0;
public void toString(){}</pre>

<p>5、 常量名全部大写</p>A

<p>如：</p><pre>public static final String GAME_COLOR="RED";</pre>

<p>6、所有命名规则必须遵循以下规则：</p>
<ul><li>
1)、名称只能由字母、数字、下划线、$符号组成
</li><li>
2)、不能以数字开头
</li><li>
3)、名称不能使用JAVA中的关键字。
</li><li>
4)、坚决不允许出现中文及拼音命名。
</li></ul>
 
<p><strong>
二、注释规范</strong></p>

<p>1、类注释</p>

<p>在每个类前面必须加上类注释，注释模板如下：</p>

<pre>/**
* Copyright (C), 2006-2010, ChengDu Lovo info. Co., Ltd.
* FileName: Test.java
* 类的详细说明
*
* @author 类创建者姓名
* @Date    创建日期
* @version 1.00
*/</pre>

 

<p>2、属性注释</p>

<p>在每个属性前面必须加上属性注释，注释模板如下：</p>

<pre>/** 提示信息 */
private String strMsg = null;</pre>

 

3、方法注释

<p>在每个方法前面必须加上方法注释，注释模板如下：</p>

<pre>/**
* 类方法的详细使用说明
*
* @param 参数1 参数1的使用说明
* @return 返回结果的说明
* @throws 异常类型.错误代码 注明从此类方法中抛出异常的说明
*/</pre>

<p>4、构造方法注释</p>

<p>在每个构造方法前面必须加上注释，注释模板如下：</p>

<pre>/**
* 构造方法的详细使用说明
*
* @param 参数1 参数1的使用说明
* @throws 异常类型.错误代码 注明从此类方法中抛出异常的说明
*/</pre>

 

<p>5、方法内部注释</p>

<p>在方法内部使用单行或者多行注释，该注释根据实际情况添加。</p>

<p>如：</p>
<pre>//背景颜色
Color bgColor = Color.RED</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">jinling</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;jinling</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;103***5512@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://www.cnblogs.com/maowang1991/archive/2013/06/29/3162366.html">&nbsp;&nbsp;参考地址</a></p></div></span>5年前 (2018-01-07)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-23584"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;ycxchkj</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;xch***163.com</p></div><div id="runoobvote-id-23584" data-commid = "23584" class="upvotejs"><a class="upvote"></a> <span class="count">151</span></div></div><div class="comt-main" id="div-comment-23584"><p><strong>Java编程规范</strong></p>

<p><strong>package的命名:</strong> package 的名字由全部小写的字母组成，例如：com.runoob。</p>

<p><strong>class和interface的命名:</strong> class和interface的名字由大写字母开头而其他字母都小写的单词组成，例如：Person，RuntimeException。</p>

<p><strong>class变量的命名:</strong> 变量的名字用一个小写字母开头，后面的单词用大写字母开头,例如：index，currentImage。</p>

<p><strong>class 方法的命名:</strong> 方法的名字用一个小写字母开头，后面的单词用大写字母开头,例如：run()，getBalance()。</p>

<p><strong>staticfinal变量的命名:</strong> static final变量的名字所有字母都大写，并且能表示完整含义。例如：PI，PASSWORD。</p>

<p><strong>参数的命名:</strong> 参数的名字和变量的命名规范一致。</p>

<p><strong>数组的命名:</strong> 数组应该总是用这样的方式来命名：byte[] buffer。</p>

<p>养成良好的编程习惯，是一个合格程序员必备的条件！加油！</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">ycxchkj</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;ycxchkj</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;xch***163.com</p></div></span>5年前 (2018-01-27)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-25175"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;你看见我ID了</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;112***0112@qq.com</p></div><div id="runoobvote-id-25175" data-commid = "25175" class="upvotejs"><a class="upvote"></a> <span class="count">183</span></div></div><div class="comt-main" id="div-comment-25175"><p><b>一个完整的Java。源程序应该包括下列部分：</b></p><ul><li><b>&nbsp;package语句，该部分至多只有一句，必须放在源程序的第一句。</b></li><li><b>&nbsp;import语句，该部分可以有若干import语句或者没有，必须放在所有的类定义之前。</b></li><li><b>&nbsp;public classDefinition，公共类定义部分，至多只有一个公共类的定义，Java语言规定该Java源程序的文件名必须与该公共类名完全一致。</b></li><li><b>&nbsp;classDefinition，类定义部分，可以有0个或者多个类定义。 </b></li><li><b>interfaceDefinition，接口定义部分，可以有0个或者多个接口定义。</b></li></ul>
<p>例如：</p>

<pre>package javawork.helloworld;
/*把编译生成的所有．class文件放到包javawork.helloworld中*/
import java awt.*;
//告诉编译器本程序中用到系统的AWT包
import javawork.newcentury;
/*告诉编译器本程序中用到用户自定义的包javawork.newcentury*/
 public class HelloWorldApp{...｝
/*公共类HelloWorldApp的定义，名字与文件名相同*/ 
class TheFirstClass｛...｝;
//第一个普通类TheFirstClass的定义 
interface TheFirstInterface{......}
/*定义一个接口TheFirstInterface*/</pre>
<p><strong>package语句：</strong>由于Java编译器为每个类生成一个字节码文件，且文件名与类名相同因此同名的类有可能发生冲突。为了解决这一问题，Java提供包来管理类名空间，包实 提供了一种命名机制和可见性限制机制。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">你看见我ID了</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;你看见我ID了</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;112***0112@qq.com</p></div></span>5年前 (2018-03-18)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-43602"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;admin</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;125***7748@qq.com</p></div><div id="runoobvote-id-43602" data-commid = "43602" class="upvotejs"><a class="upvote"></a> <span class="count">160</span></div></div><div class="comt-main" id="div-comment-43602"><p><strong>数据类型的溢出</strong></p>

<p>在 Java 中，只有数字类型才能参与运算。但是每个数据类型都有他的取值范围。</p>

<p>例如 byte 数据类型，它的取值范围为 <span class="marked">-128 - 127</span> 。</p>

<p>当我们使用 <span class="marked">byte  b  =  128;</span> 时，肯定会报错。</p>

<p>但是使用 <span class="marked">byte b  =   127+1;</span>  并不会报错。</p>

<p>而且运算的结果为 <strong>-128</strong>。</p>

<p>我们可以向数据类型的取值范围看作是一个圆，每多一个数据向前移动一个，当数据达到最大值时，我们再加 1，可以就会变成最小值，这就是数据的溢出。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">admin</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;admin</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;125***7748@qq.com</p></div></span>4年前 (2019-06-13)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-45389"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;hhh</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;945***651@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://www.cnblogs.com/shizunatsu/p/10617346.html">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-45389" data-commid = "45389" class="upvotejs"><a class="upvote"></a> <span class="count">148</span></div></div><div class="comt-main" id="div-comment-45389"><p><strong data-title>byte 取值范围</strong></p>
<p>Java 中，byte 占一个字节，取值范围为何是 <span class="marked">-128~127？（-2^7~2^7-1）</span></p>

<p>计算机是用二进制来表示数据的，一个字节也就是 8 个比特位，其中最高位表示符号位（0 正 1 负）。</p>

<p>故 byte 的取值范围为 <strong>1000 0000</strong> 到 <strong>0111 1111</strong>。</p>

<p>在 Java 中，是采用补码来表示数据的。</p>

<p>正数的补码和原码相同，负数的补码是在原码的基础上各位取反然后加 1。</p>

<p>1000 000 是补码，减一然后按位取反得到其原码 1000 0000。（减一得 0111 1111，再按位取反得 1000 0000）</p>



<p>因为是负数，所以最小的 byte 值为 <strong>-2^7=-128</strong>。</p>

<p>0111 1111 的十进制为 2^7-1=127（等比序列求和）。</p>

<p>byte 是一个字节，共有 2^8=256 种可能性，也就是 -128~127。</p>

 

<p>其他基本数据类型同理：</p>

<p>char 没有负值，占两个字节，所以取值范围是 <strong>0~2^16-1（65535）</strong>。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="../note/45389">hhh</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;hhh</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;945***651@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://www.cnblogs.com/shizunatsu/p/10617346.html">&nbsp;&nbsp;参考地址</a></p></div></span>4年前 (2019-08-03)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-56970"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;璀璨流星雨</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;198***6202@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://blog.csdn.net/weixin_38011265/article/details/79149313">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-56970" data-commid = "56970" class="upvotejs"><a class="upvote"></a> <span class="count">122</span></div></div><div class="comt-main" id="div-comment-56970"><p><strong>throw 和 throws 的区别：</strong></p><p>
throws 用来声明一个方法可能产生的所有异常，不做任何处理而是将异常往上传，谁调用我我就抛给谁。</p>
<p>throw 则是用来抛出一个具体的异常类型。</p>
<p>
throws 在方法后边声明异常，其实就是自己不想对异常做出任何的处理，告诉别人自己可能出现的异常，交给别人处理，让别人处理。</p><p>
throw 就是自己处理一个异常，有两种方式要么是自己捕获异常 <strong>try...catch</strong> 代码块，要么是抛出一个异常（throws 异常）。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">璀璨流星雨</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;璀璨流星雨</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;198***6202@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://blog.csdn.net/weixin_38011265/article/details/79149313">&nbsp;&nbsp;参考地址</a></p></div></span>3年前 (2020-09-11)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-74900"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;cxy</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;597***644@qq.com</p></div><div id="runoobvote-id-74900" data-commid = "74900" class="upvotejs"><a class="upvote"></a> <span class="count">16</span></div></div><div class="comt-main" id="div-comment-74900"><p>1、java文件通过<b>java编译器</b>把<b>.java</b>文件编译为<b>.class文件</b></p><p>2、<b>.class</b>文件通过<b>java虚拟机(JVM)</b>传送指令给<b>解释器</b></p><p>3、<b>解释器</b>将指令翻译成<b>特定机器</b>上的目标<b>机器码</b>，进行运行</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">cxy</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;cxy</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;597***644@qq.com</p></div></span>8个月前 (08-29)</div></div></li><!-- #comment-## -->
<li class="comment byuser comment-author-tianqixin bypostauthor odd alt thread-odd thread-alt depth-1" id="comment-76841"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;恋未遂</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;170***3913@qq.com</p></div><div id="runoobvote-id-76841" data-commid = "76841" class="upvotejs"><a class="upvote"></a> <span class="count">13</span></div></div><div class="comt-main" id="div-comment-76841"><p>补充一下，其实自己在进行编译的时候，标识符是可以用中文的，如下所示的类名就可以为中文：</p>

<pre>package 自学1;
public class 你好{
public static void main(String[]args) {
    System.out.println("你好");
   }
}</pre>
并不是很死板，真的如规定所说的那样。<div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">恋未遂</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;恋未遂</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;170***3913@qq.com</p></div></span>5个月前 (12-12)</div></div></li><!-- #comment-## -->
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});
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